The effect of polymer polarity on the microwave absorbing properties of MWNTs

Two different polarity polymers, polyvinylpyrrolidone (PVP) and polyethyleneimine (PEI) with the same molecular weight were selected to modify the surface of MWNTs using a non-covalent method. The aim was to investigate the effect of polymer polarity on the microwave absorbing properties of MWNTs. The polarization effects of PVP and PEI on MWNTs were simulated by the Cole-Cole semicircle model. The structure and morphology of polymer modified MWNTs were characterized by FTIR, TGA, Raman spectroscopy, SEM and TEM. The SEM and TEM results demonstrated that the addition of PVP and PEI could prevent MWNTs from aggregating and was helpful for the improvement of the dispersion of MWNTs. The excellent microwave absorbing properties could be obtained by adjusting the mass percentage of polymer/MWNTs hybrids in paraffin wax. The results showed that both PVP/MWNTs and PEI/MWNTs hybrids had good microwave absorption (<-7 dB) in the X-band frequency when the mass percentage of polymer/MWNTs in paraffin wax was 30%. However, the maximum reflection loss (RL) of PVP/MWNTs hybrids was larger than that of PEI/MWNTs hybrids. The maximum RL of PVP/MWNTs was -23.84 dB, while the maximum RL of PEI/MWNTs was about -21.01 dB. Moreover, the polymer polarity had an impact on the response frequency where the maximum RL appeared. The RL peak values of PVP/MWNTs hybrids appeared at 10.48 GHz, while it was at 8.96 GHz for the PEI/MWNTs hybrids. The results indicated that the polymer polarity had a significant influence on the microwave absorbing properties and microwave absorbing response frequency of MWNTs.